Brain functional activities include several procedures like neuronal activity and local energy metabolism, and complicated functional activities enable the brain to bring together information of multiple modes, among which electrical activities of neurons and changes in blood oxygen metabolism in active areas are the most important, and only by effectively extracting, analyzing and combining said two kinds of information, can the brain functional activities be organically linked to each other. Currently, combining the nerve electrophysiological equipment and the metabolic process detection equipment to make full use of the advantages thereof has become an important means for deeply detecting and understanding neural information.
The system intends to realize integration of the three functions of near-infrared spectrometer, electroencephalograph and fusion device of near-infrared spectrum and electroencephalograph on one instrument through an effective combination of the functional near-infrared spectroscopy technology and the EEG collection technology, thereby realizing functions like synchronizing or separate collecting of the neural electrical activity and blood oxygen supply information in brain areas.
The electroencephalography (EEG) technology obtains functional information of the brain mainly through measuring changes in electrical activities of the brain neurons, and it has a very high time resolution (ms). Currently, the EEG systems of such companies as NeuroScan, Brain Products GmbH of Germany and EGI of the USA are widely used because they have higher collection accuracy.
The functional Near-infrared spectroscopy (fNIRS) technology is a noninvasive and novel brain function imaging method developed since the 1970s. Its detection principle is to realize detection of functional activities of the cerebral cortex based on the fact that the near-infrared light can well penetrate the brain tissues. Since oxy-hemoglobin and deoxy-hemoglobin have different absorption characteristics of infrared light, the fNIRS measures changes in the intensity of light entering into the cerebral cortex and the intensity of light outcoming from the cerebral cortex tissues after having been scattered and absorbed so as to reflect changes in blood oxygen metabolism in the cerebral cortex. Compared to fMRI, fNIRS has higher time resolution (ms) and is less sensitive to movement; meanwhile, it is light, portable, safe, relatively cheap and can be used for long-time clinical monitoring. Currently, the dominating systems in the market are series ETG-4000 to ETG-7000 systems from Hitachi; systems FOIRE-3000 and OMM-2001 from SHIMADZU Corporation; system CW5 from TechEn (a U.S. company); systems DYNNIRI 932 and Dynot from NIRx medical tech corporation; and system OXYMON MKIII from Artinis (a Dutch company); etc.
Although there have been many devices or system in the market for detecting brain activities, they usually have the following deficiencies:
1) The EEG technology is relatively well developed, but some key technologies still need to be improved, for example, the existence of DC drift during brain electricity collection will easily make the amplifier to work in a saturation state, the existence of common mode interference limits accuracy of the collected data, and the problem of limited frequency bandwidth during brain electricity collection, so a new type full band collection system needs to be developed.2) Improvements to the NIRS system mostly concern such technical levels as appearance, interface and wireless communication, but no impressive progress has been achieved in fundamental researches on relevant technical problems. Besides, development of the NIRS system in China has been falling behind among nations.3) Usually, they are all measuring technologies based on a single mode, for example, the EEG only collects electrical activities of the brain neurons, and the fNIRS only collects changes in blood oxygen metabolism in active areas. On the one hand, the manufacturers only focus on manufacturing single-mode measuring systems, and they are not proficient in measurement of other modes; on the other hand, a dual-mode joint collection system has hardware integration cost and design difficulties concerning data synchronous fusion. Up to now, there has not been any photoelectrically synchronous detection device or system at home and abroad yet, nor has any corresponding patent been found.4) With the progress achieved in science and technology in recent years and out of the urgent clinical needs, there are more and more fundamental researches and application researches on combining the EEG technology and the near-infrared technology, but the current researches are mostly about simply arranging the EEG electrodes and near-infrared optrodes in a cross manner in a certain brain area, and enabling the two independent systems of EEG system and near-infrared system to collect separately through external triggering, and then registering and fusing the two kinds of data in later data analysis. Such a simple design has the following characteristics: first, it does not realize coupling between the electrodes and the optrodes; second, usually the difference of sampling frequencies of the two independent collection systems is great, and they do not achieve synchronous collections of the brain electrical signals and the blood oxygen signals at the same point of the scalp. In addition, in subsequent data analysis process, the time points of the two kinds of signals are usually matched by means of down-sampling or interpolation, so fusion of the EEG data and near-infrared data are not truly realized. Hence, development in fundamental research and clinical application is severely hindered.